The continuing trend of scaling down integrated circuits has forced the semiconductor industry to consider new techniques for fabricating precise components at submicron levels. Along with the need for smaller components, there has been a growing demand for devices requiring less power consumption. In the manufacture of transistors, these trends have led the industry to refine approaches to achieve thinner cell dielectric and gate oxide layers.
In dynamic semiconductor memory storage devices it is essential that storage node capacitor cell plates be large enough to retain an adequate charge (or capacitance) in spite of parasitic capacitance and noise that may be present during circuit operation. As is the case for most semiconductor integrated circuitry, circuit density is continuing to increase at a fairly constant rate. The issue of maintaining storage node capacitance is particularly important as the density of DRAM arrays continues to increase for future generations of memory devices.
The ability to densely pack storage cells while maintaining required capacitance levels is a crucial requirement of semiconductor manufacturing technologies if future generations of expanded memory array devices are to be successfully manufactured.
One method of maintaining, as well as increasing, storage node size in densely packed memory devices is through the use of "stacked storage cell" design. With this technology, two or more layers of a conductive material such as polycrystalline silicon (polysilicon or poly) are deposited over an access device on a silicon wafer, with dielectric layers sandwiched between each poly layer.
Though stacked (capacitor) storage cells are promising candidates to achieve sufficient storage capacitance in a limited area, as the DRAM cell size shrinks, scaling of the stacked capacitor structures is becoming more difficult.
Storage capacitance can be enhanced by using Hemi-Spherical Grain (HSG) silicon to form the storage node electrode without increasing the area required for the cell or the storage electrode height. Some available methods include those methods disclosed in U.S. Pat. Nos. 5,407,534, 5,278,091 and 5,340,765, which are hereby incorporated by reference.